Solvents play an important role in fields such as paint, adhesive, and printing ink. Solvents are naturally required to have high dissolving power for solutes. In the above fields, solvents also have substantial effects on performances such as wettability for surfaces to be coated and drying property.
As solvents used together with resins commonly used in paint, adhesive, printing ink, and other fields, such as cellulose resin, epoxy resin, acrylic resin, vinyl acetate resin, vinyl chloride resin, alkyd resin, and polyester resin, there has been conventionally used cellosolves which are glycol ethers, particularly cellosolve acetate with appreciation of its excellent performances. However, due to recent very stringent requirement for safety of chemical substances in consideration of problems such as pollution, restriction for use of cellosolve acetate has been tightened because of its toxicity, and the concentration control standard for working environment has been established by the Labor Safety and Hygiene Law.
Therefore, development has been actively pursued for alternative solvents having high dissolving power comparable to cellosolve acetate and no concern about safety. For instance, solvents such as ethyl lactate, propylene glycol monomethyl ether acetate, methoxypropanol, and ethyl β-epoxypropionate are under study as prospective alternative solvents, but they are not fully satisfactory in dissolving power, safety, odor, handleability, or the like. Among them, ethyl lactate, which is approved as a food additive, is considered as most preferable in terms of safety but not quite satisfactory in dissolving power for high-molecular-weight compounds or various additives.
In terms of dissolving power, alkyl β-alkoxypropionates such as methyl β-methoxypropionate and ethyl β-ethoxypropionate are considered as most preferable, but they are not yet satisfactory in dissolving power for high-molecular-weight compounds or various additives, and not satisfactory in volatility after application, either.
In addition to uses as described above, solvents are also used for cleaning cutting oil, process oil, press oil, rust-preventive oil, lubricant oil, and oils used as grease, pitch, or the like; for cleaning solder flux, ink, liquid crystals, etc.; and for other purposes. For such cleaning purpose, there are commonly used solvent compositions mainly composed of halogen-containing solvents such as CFC-113 (1,1,2-trichloro-1,2,2-trifluoroethane), methylchloroform (1,1,1-trichloroethane), and trichloroethylene. Especially, CFC-113 has been widely used because of its nonflammability, low toxicity, and hence high safety, and also because CFC-113 can selectively dissolve various contaminants while not damaging metals, plastics, elastomers, or the like. However, because CFC-113 and methylchloroform destruct ozone layer in the stratosphere, which is a cause of skin cancer, the use thereof has been rapidly restricted. Use of trichloroethylene has been also restricted from safety viewpoint because of problems such as suspicion of carcinogenicity.
Therefore, development is actively conducted for CFC-substitute cleaning agents with excellent cleaning capability comparable to CFC-113 and the like and no concern about ozone layer destruction. For example, Patent Document 1 proposes a cleaning agent comprising 1,2-difluoroethane as a main component. Patent Document 2 proposes a mixture of 1,1-dichloro-2,2,2-trifluoroethane and dimethoxybenzene, while Patent Document 3 proposes a cleaning agent comprising hexafluorobenzene as a main component. However, these solvents are inferior in performance to CFC-113, and the use of these halogen-containing solvents will become wholly restricted in the future because of environmental and safety problems.
Patent Document 1: Japanese Patent Laid-open Publication H1-132694
Patent Document 2: Japanese Patent Laid-open Publication H2-178396
Patent Document 3: Japanese Patent Laid-open Publication H3-167298